Process for making bromine cyanide



March 21, 1950 R. H. HARTIGAN PROCESS FOR MAKING BROMINE CYANIDE Filed Sept. 19, 1946 NORMALITY H $0 50LUTI0N CHARGED loo Fzwu Nam 62 295 58 H R W 0.5 NORMALITY H 50 SOLUTION CHARGED zmu awn 62 295 .50.?

Y. E N e m r u a INVEN OE.

N w mm W. H H w W h r m Patented Mar. 21, 1950 UNITED STATES PATENT FFICE PROCESS FOR MAKING BROMINE CYANIDE Raymond H. Hartigan, Pittsburgh, .Pa., assignor to Koppers Company, Inc., Pittsburgh, Pa, a corporation of. Delaware Application September 19, 1946, Serial No. 697,956

Claims. 1

This invention relates to cyanogen bromide. More particularly the invention relates to the manufacture of cyanogen bromide by the bromination of sodium cyanide.

Cyanogen bromide is a solid at ordinary atmospheric temperatures having a melting point of 52 C. and a boiling point of 612 C. This solid material, therefore, may be advantageously handled and used for the manufacture of cyanuric bromide and melamine.

In volume XI, Organic Synthesis (1931) page 30, Hartman and Dreger describe a process for the bromination of sodium cyanide directly with elemental bromine. The yields of cyanogen bromide obtained by their process vary from 73% to 85% of the theoretical cyanogen bromide available.

The primary object of the present invention is to provide a process of brominating sodium cyanide to obtain a substantially theoretical yield of cyanogen bromide.

Another object of the invention is to provide a process by which sodium cyanide may be easily brominated without the loss of products to obtain a high quality cyanogen bromide.

With these and other objects in view, the in I A part of the cyanogen bromide prepared as in Equation. 1 may be decomposed by hydrolysis to ammonium bromide in accordance with the fol lowing equation:

Further cyanogen bromide may have a metathetical reaction with sodium cyanide in accordance with the following equation:

Some of the cyanogen formed by Equation 3v may, in turn, hydrolyze to azulmic acid and other products in accordance with equation:

Furthermore sodium cyanide may react with water to produce a formats in accordance with the equation:

NaCN+2H2O=HCOONa+NHs From Equations 1, 2 and 3 above "it will be seen that the bro-mine which is not combined with the cyanogen radical as cyanogen bromide appears as inorganic bromides, such as HBr, NaBr and NHiBr, and the yield of cyanogen bromide formed in the reaction is substantially reduced.

The reaction of Equation 2 is catalyzed by acid; The reaction of Equation 3 takes place in a neu-, tral solution. Accordingly when the synthesis of cyanogen bromide is conducted in a sulphuric acid solution the reactions shown iii-Equations 3 and 4. are avoided. Furthermore, it is found that the reaction in Equation 5 is insignificant with a dilute acid solution.

The presence of acid during the reaction forms an important part of the present invention. Furthermore, it has been found that the strength of acid in the reaction mixture is very important in obtaining the most efiicient reaction and the maximum yield. Experiments have shown that substantiallytheoretical yields may be obtained with 0.5 to 8.0 normal sulphuric acid present in the reaction mixture. Expressed in another way, the distillation residue should have a 0.3 to 4.3 normal sulphuric acid acidity.

In the absence of acid (preferably a mineral acid) it is probable that sodium cyanide and cyanogen bromide react to consume the cyanogen bromide. Furthermore in the absence of acid and with an excess of sodium cyanide, the sodium cyanide reacts with .the cyanogen bromide to give a. quantitative destruction of the cyanogen bromide.

To carry out the process in accordance with the preferred form of the invention the materials are'reacted in they following proportions: one mol of bromine is added to 150 ml. of 2 normal sulphuric acid solution which is preferably placed within a mixer that may be provided with a cooling coil ora cooling jacket. The bromine mixture is cooled to a'tempe'rature of approximately 20 C. and to it is added 52-54 grams of sodium cyanide pure) dissolved in ml. of water; The sodium cyanide solution is slowly added to the bromine mixture and the reactants are mixed and cooled to -maintain the temperature below 23 (3. -'At the end of the reaction a clear solution of sodium bromide is formed in which a major portion of the cyanogen bromide is precipitated as white crystalline cyanogen bromide.

When the reaction is completed the cyanogen bromide may be directly distilled out of the reaction mixture. The reaction mixture contains a large amount of water and his important to exclude water from the cyanogen bromide'if' a TABLE I The preparation of cyanogen bromide from bromine and sodium cyanide in a sulphuric acid medium [Efiect of high acidity on the yield] i g T t l B ON 2 4 o a r Moles Solution Mol. Per cent Charged In Table II are shown the yields of cyanogen bromide which are produced by the bromination of sodium cyanide when the strength of sulphuric acid is normal or less than normal.

TABLE II The preparation of cyanogen bromide from bromine and sodium cyanide in a dilute sulphuric acid medium {Eflect oi low acidity on the yield] Normality T t 1 B 1 H280I o a r l Charged Mol. Per Cent In Table III is illustrated the efiect of 30% excess of sodium cyanide on the yield of cyanogen bromide obtained when directly brominating sodium cyanide with elemental bromine without acid present and the bromination of the same amount of sodium cyanide under the same conditions when having 4-normal H2804 present.'

TABLE III Preparation of cyanogen bromide from bromine and 30% excess sodium cyanide Run l67 g. NaCN dissolved in 110 ml. H1O; 51.8 ml. Bra; 150 ml.

L-N H1504. 'fiadlll 267 g. NeCN dissolved in 110 ml. HaO; 51.8 ml. Bra; 150 ml. a

Normality Run Size of Run, H2804 fig Moles Solution e Charged These runs illustrate clearly the advantage of the presence of sulphuric acid in the reaction mixture.

The data of Table III show that an excess of 30% sodium cyanide in run 2, a practically quantitative amount of cyanogen bromide is destroyed. In run 1 when using the 30% excess of sodium cyanide sufi'icient sulphuric acid is present to take care of the entire excess of sodium cyanide, and therefore a substantially quantitative yield of cyanogen bromide is secured. It is important, therefore, to have present in the reaction mixture sumcient acid to react with the excess sodium cyanide in order to obtain the maximum yield of cyanogen bromide. A large number of tests have been made using stoichiometric proportions of bromine and sodium cyanide. It has been found that in such runs the yield of cyanogen bromide is between four and five percent lower than when sulphuric acid is present. It is desirable when obtaining the maximum yields of cyanogen bromide to use slight excess of sodium cyanide and have sufficient acid present in the reaction to take care of the excess sodium cyanide.

The graphs shown in the drawings are curves which are plotted from the data of Tables I and II. Figure l is made from the data of Table I and Figure 2 is made from the data of Table II. These graphs show the yield of cyanogen bromide produced by reactions taking place in different strengths of sulphuric acid. These curves illustrate clearly the fact that the use of 0.5 to 8 normal sulphuric acid gives an important and increased yield of product.

A large number of experiments have shown that in the absence of the sulphuric acid in the reaction mixture approximately 31% of the bromine is not recovered as cyanogen bromide when an excess of 30% sodium cyanide is used.

Experiments have also shown that if the reaction takes place in the presence of an alkali the cyanogen bromide is destroyed quantitatively.

The preferred form of the invention having been thus described, what is claimed as new is:

-.1. A process of making cyanogen bromide consisting in slowly reacting sodium cyanide with bromine water in the presence of an added reagent consisting of sulphuric acid having a concentration of 0.5 to 8.0 normal.

2. The process of making cyanogen bromide consisting in cooling bromine water to a temperature of approximately 20 C., slowly adding a water solution of sodium cyanide while maintaining a temperature below 23 C. in the presence of an added reagent consisting of sulphuric acid having a concentration between 0.5 and 8.0 normal.

3. The process defined in claim 2 in which the sulphuric acid concentration in the residue mixture is 0.3 to 4.3 normal.

4. A process of making cyanogen bromide while avoiding anoxidation reaction consisting in: cooling a mixture of bromine and sulphuric acid having a concentration between 0.5 and 8.0 normal to a temperature of approximately 20 C., slowly adding a reagent consisting of a water solution of sodium cyanide while maintaining the temperature of the reaction mixture below 23 C., thereafter distilling the reaction mixture and removing cyanogen bromide through a fractionating tower containing a drying agent to recover a dry cyanogen bromide.

5. The process of making cyanogen bromide consisting in: cooling bromine water to a temperature of approximately 20 C., slowly adding a water solution of sodium cyanide while maintaining a temperature below 23 C. in the presence of an adde'd reagent consisting of sulphuric 5 I" 6 acid having a concentration between 0.5 and 8 FOREIGN PATENTS normal, and distilling cyanogen bromide out of the reaction mixture. Number Country D RAYMOND H. HARTIGAN. ,710 Great Britain Of 1900 REFERENCES CITED OTHER REFERENCES The followin references are of record in the cyarpgen COmPOuHdS'" by Williams; me of this paint: Churchill, London (1915), pages a and 7.

UNITED STATES PATENTS 10 Number Name Date 666,135 Goepner et a1 Jan. 15, 1901 1,938,324 Dieterle Dec. 5, 1933 

1. A PROCESS OF MAKING CYANOGEN BROMIDE CONSISTING IN SLOWLY REACTING SODIUM CYANIDE WITH BROMINE WATER IN THE PRESENCE OF AN ADDED REAGENT CONSISTING OF SULPHURIC ACID HAVING A CONCENTRATION OF 0.5 TO 8.0 NORMAL. 